Legend has it that when none of the birds are left, the kingdom is in peril - at one point during the Blitz all but one died "of fright". Now Yeoman Warder Ravenmaster Derrick Coyle has been forced to quarantine his six royal charges in specially built aviaries within the Norman fortress.

The ravens shouldn't mind much. Coyle told the BBC last year: "I have a great relationship with the birds."

Bird flu has yet to be confirmed in either wild or captive species in the UK - the nine suspicious swans reported across Britain over the weekend have all tested negative for the disease.